Electrical inductive apparatus having rigid foam supporting members and methods of providing same

ABSTRACT

A power transformer having rigid plastic foam support blocks and rods. A support block located between the magnetic core and the core supporting structure is formed by injecting a plastic foam material into an expandable container and forming the container of foam in a mold located in the transformer where the molded support block is to remain. The foam expands and then solidifies when the block has the proper shape. A support rod located between the magnetic core and the winding structure disposed thereon is constructed by placing a flexible, substantially nonexpandable tubular member between the core and the winding structure, injecting a plastic foam material into the tubular member, and allowing the foam material in the tubular member to expand and force the tubular member tightly against the core and the winding structure.

I Jan. 1, 1974 3,634,798 1/1972 Astleford, 336/60 X 3,419,134 12/1968264/65 X Primary ExaminerThomas .l. Kozma Attorney-A. T. Stratton et a1.

[57] ABSTRACT A power transformer having rigid plastic foam supportblocks and rods. A support block located between the magnetic core andthe core supporting structure is formed by injecting a plastic foammaterial into an expandable container and forming the container of foamin a mold located in the transformer where the molded support block isto remain. The foam expands and then solidifies when the block has theproper shape. A

support rod located between the magnetic core and the winding structuredisposed thereon is constructed by placing a flexible, substantiallynon-expandable tubular member between the core and the windingstructure, injecting a plastic foam material into the tubular member,and allowing the foam material in the tubular member to expand and forcethe tubular member tightly against the core and the winding structure.

11 Claims, 12 Drawing Figures 336/196, 29/602, 264/45, 336/60, 336/198,336/210 H0lf 27/30 336/60, 196, 197,

Cahon et a]. Feather et a ll a.

United States Patent [191 Morris, Jr. et a1.

l l ELECTRICAL INDUCTIVE APPARATUS HAVING RIGID FOAM SUPPORTING MEMBERSAND METHODS OF PROVIDING SAME [75] Inventors: Louis Morris, Jr.,Campbell; Donald R. Slanina, Youngstown, both of Ohio; Martin P. Seidel,Monroeville, Pa.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

Jan. 9, 1973 [22] Filed:

[21] Appl, No.: 322,237

[51] Int. [58] Field of Search.....................

[56] References Cited UNITED STATES PATENTS PMENTEUJAN H974 sum 1 or 4PAIENIEU I I974 FIG. 9

FIG. II

saw u or 4 SELECTING A FLE XI BLE. SUBSTANTIALLY NON-EXPANDABLE TUBULARMEMBER HAVING SUITABLE DIMENSIONS INSERTING THE TUBULAR MEMBER BETWEENTHE CORE AND THE WINDING TUBE 'INSERTING A FOAM MATERIAL INTO THE-TUBULAR MEMBER ALLOWING THE FOAM MATERIAL TO EXPAND ELECTRICAL INDUCTIVEAPPARATUS HAVING RIGID FOAM SUPPORTING MEMBERS AND METHODS OF PROVIDINGSAME BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates, in general, to electrical inductive apparatus and,more specifically, to power transformers having foam supporting membersand methods of providing same.

2. Description of the Prior Art Power transformers of the core-form typehave magnetic cores which have a stepped cross-sectional shape in theleg and yoke regions of the core. Known generally in the art ascruciform cores, the primary purpose of the steps is to shape the legsof the core closely to the circular shape of the windings disposedthereon.

Difficulties in transformer design and construction are brought about bythe use of cruciform cores. Such transformers include a frame orsupporting structure which helps clamp the core laminations together andwhich helps prevent movement of thelaminations during shipment of thetransformer. Support blocks are located between the core and the framestructure. The support blocks are stepped to conform to the shape of thestepped core. However, since variations in the construction of the corescauses the shape of the steps of each core to be different, theuse ofconventional support blocks having fixed step dimensions does notsupport each lamination equally.

Therefore, it is desirable, and it is an object of this invention, toprovide a transformer having core support blocks which conveniently andaccurately conform to the stepped dimensions of the magnetic core.

Another difficulty frequently encountered in cruciform-type magneticcore transformers is the means for supporting the winding structuresfrom the core legs. According to the prior art, each winding structureis mounted on a winding tube. The winding tube is positioned around oneof the core legs and secured thereto with the aid of wooden or glassepoxy dowel rods inserted between the winding tube and the core steps.

WIth the use of dowel rods, workmanship must be highly accurate toconstructa supporting structure for the winding which'will withstand themechanical forces produced under short-circuit conditions. The propersize of rod must be selected from the finite number of sizes available,thus most rods selected are only near the proper size. Non-uniformity ofthe rod and of the space it is inserted into make it impossible tosupport the winding tube equally at all points using conventional rods.This allows the windings'to flex inward under short-circuit conditionsthereby disrupting the insulation thereon which may eventually result intransformer failure due to a shorted winding.

Therefore, it is desirable, and it is an object of this invention, toprovide a transformer having winding support rods which conveniently andaccurately conform to the distance between the winding tube and themagnetic core.

SUMMARY OF THE INVENTION There is dislosed herein new and usefultransformer support components and methods of constructing thecomponents. Stepped support blocks are formed between the magnetic coreand the supporting structure positioned therearound. Forming the blocksinvolves inserting an expandable foam material into an expandablecontainer. The contairier of foam is formed by a mold which ispositioned adjacent to the core and the supporting structure. As thefoam material expands, the foam material in the container fills thevolume within the mold. When the foam material solidifies, the mold isremoved, leaving a support block which is tightly and evenly forcedagainst the core and the supporting structure.

The winding structures of the transformer are supported from themagnetic core by rods constructed mainly of foam material. Each rod isconstructed by inserting a flexible, substantially non-expandabletubular member between the winding tube of the winding structure and thecore leg. An expandable foam material is inserted into the tubularmember and allowed to expand. The dimensions of the tubular member areselected to allow it to tightly push against the winding tube and thecore leg when the foam material expands. Rods constructed according tothis embodiment automatically conform to different separation distancesbetween the core and the winding tube; thus, the winding tube issupportedequally along its axis by the foam support rod.

' BRIEF DESCRIPTION OF THE DRAWING Further advantages and uses of thisinvention will become more apparent when considered in view of thefollowing detailed description and drawing, in which:

FIG. 1 is a view illustrating a transformer having support blocksconstructed according to this invention;

FIG. 2 is a partial view illustrating the position of a support blockmold adjacent to a core yoke;

FIG. 3 is an exploded view of a support block mold;

FIG. 4 is a cut-away view of a support block constructed according tothis invention;

FIG. 5 is a flow chart of steps performed in constructing a supportblock according to this invention;

FIG. 6 is a partial view illustrating the position of a support blockmold adjacent to a core leg;

FIG. 7 is across-sectional view of a winding supported from a core legby support rods constructed according to this invention;

FIG. 8 is a view illustrating a step in the construction of a supportrod;

FIG. 9 is a partial view illustrating an imaginary circle between thecore and the winding tube used in defining the proper size of thetubular member of the support rod;

FIG. 10 is a partial view illustrating the tubular member before thefoam material is inserted therein;

FIG. 11 is a partial view illustrating the tubular memher after the foammaterial has been inserted therein and has expanded; and

FIG. 12 is a flow chart of steps performed in constructing a support rodaccording to this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the followingdescription, similar reference characters refer to similar elements ormembers in all the figures of the drawing.

20. Additional bushings would normally be mounted on the casing 14 bythe bushing attachments 22 and 24.

The magnetic core 12 is enclosed by a frame structure 26 which includesthe end frames 28, 30, 32 and 34, lock plates, such as the lock plate36, and the punching braces 38. A winding structure 40 is disposedaround one of the legs of the core 12. Similar winding structures wouldnormally be disposed around the core legs 42 and 44 in a completetransformer of the type shown in FIG. 1.

The punchings of the magnetic core 12 are secured in position by supportblocks 46 which are located between and tightly against the punchingbraces 38 and the outer portion of the core legs and the outer portionof the core yokes 48 and 50. The support blocks 46 are constructed ofnon-magnetic material and are shaped to conform to the stepped shape ofthe magnetic core 12. The support blocks 46 prevent slipping of the corepunchings during shipment of the transformer and distortion of thepunchings during high stress conditions.

The support blocks 46 are constructed of a suitable material which iscast into the exact shape the blocks 46 require at their fixed locationin the transformer. FIG. 2 illustrates the use of a mold positioned onthe punching brace 38. The mold 52 includes a base 54, sides 56 and 58,and bolts 60 which connect the sides to the base. FIG. 3 illustrates themold 52 in an exploded view.

A plastic foam material, such as polyurethane or epoxy materialscontaining a foaming agent, is inserted into an expandable containerconstructed of a suitable material, such as nitrile rubber. Thecontainer, with the foam material therein, is placed into the mold 52and allowed to expand. With the mold 52, one of the sides 56 and 58would be attached after the container and the foam material are disposedtherein.

lt'is within the contemplation of this invention that the foam materialmay be inserted into the container after the container has been placedin the mold 52. The foam may be inserted through a suitable opening inthe mold 52, with the opening being closed after the foam has beeninserted. Suitable high-temperature foams include sucrose basedpolyvols, aromatic amine crosslinked epoxies, and isocyaminatepolyurethanes.

FIG. 4 illustrates a support block 46 in a cut-away view. The rigidplastic foam material 62 is contained within the expandable container64. The purpose of the container 64 is to confine the expanding foammaterial within the bounds of the mold 52 and the core 12. Without theuse of such a container, it is possible for the foam material topenetrate the joint between adjacent core punchings and thereby spreadthe core laminations apart. In transformers where such penetration isnot objectionable, the container 64 may be elimi nated from the block46.

As shown in FIG. 4, the face 66 of the support block 46 is stepped toconform to the shape of the portion of the magnetic core 12 which it isadjacent to. Since pressure is developed between the surfaces of theframe structure 26 and the magnetic core 12 when the foam material 62expands, the faces of the support blocks 46 push tightly against thesesurfaces and securely hold the punchings in place. The mold 52 isremoved when the foam material 62 has become sufficiently rigid.

FIG. is a flow chart illustrating the steps performed in constructing asupport block 46. By constructing support blocks according to thismethod, irregularities in core dimensions are not troublesome since eachblock is, in effect, specifically made for its particular location.

FIG. 6 illustrates a mold 68 positioned on the leg 44 of the magneticcore 12 for forming a support block 46. The mold 68 includes thecomplementary sections 70 and '72 which are attached to the punchingbrace 38 by the bolt 74. Construction of a support block 46 between apunching brace 36 located at the end of an end frame member isaccomplished similarly to the method previously described.

As shown in FIG. 11, the winding structure 40 is disposed around a legof the magnetic core 12, and normally other winding structures would bedisposed around each of the core legs 42 and 44. Each winding structuremust be supported from the core 12 by an appropriate supportingstructure to prevent inward collapse of the winding structure duringexcessive stress conditions.

FIG. 7 illustrates, in a cross-sectional view, a winding supportingstructure which is constructed according to this invention. The windingstructure 78 is disposed on a winding tube 80. The winding tube 80 issupported from the magnetic core leg 82 by the support rods 84. Each rod84 includes a tubular member 66 containing a rigid plastic foam material88 as previously described herein. I

Several sizes of tubular members 86 must be available for selection ofthe proper tubular member 86 to form a rod 84 having appropriatedimensions. The tubular member 86 is constructed of a substantiallynonexpandable and flexible material, such as epoxy-treated glass fibercloth, rubber treated cotton cloth, on flexible resin-treated cotton orglass braid.

FIG. 8 illustrates a method of constructing a rod 84. A tubular member36 is inserted between the winding tube 80 and the core leg 82. Viscousplastic foam material 88 is inserted into the tubular member 86 by asuitable means which is symbolically indicated by pouring from thebeaker 96. A pressure system may be used to force the foam material intothe tubular member 86 which is closed at the lower end 92. When the foammaterial 68 expands, the tubular member 86 flexes to push against thewinding tube 86 and the core leg 82. When the foam material 68solidifies, a rod 84 which fits tightly against the core leg 62 and thewinding tube 80 is formed. Normally, the tubular member 86 is closed atits upper end after the foam material 88 has been inserted therein.

It is important that the tubular member 66 be constructed of asubstantially non-expandable material. However, the material must besufficiently flexible to permit a change in cross-sectional shape of thetubular member 86 as the foam material 68 expands during solidification.It is also important that the circumference of the tubular member 66have an appropriate dimension.

FIG. 9, H0 and Ill will be referred to in describing the selection ofthe proper size for the tubular member 66. FIG. 9 illustrates a circle94 having a diameter d just sufficient to allow the circle 94 totangentially touch the winding 86 at position 96 and the core leg atpositions 98 and W6. At four locations around the core leg 82, a similarcircle would be tangent to the core leg 82 at only one position sincethe core is substantially fiat with respect to the winding tube 86 atsuch positions.

FIG. illustrates a tubular member 86 having the proper dimensions andpositioned between the winding tube 80 and the core leg 82 ready forinsertion of the foam material 88. The outside circumference of thetubular member 86 must be slightly larger than the circumference of thecircle 94, which is 1rd. When the foam material 88 has been inserted andallowed to expand, the tubular member 86 receives the shape illustratedin FIG. 11. The pressure exerted by the contained foam material 88 isexerted on the winding tube 80 and the core leg 82. Since the tubularmember 86 is substantially non-expandable, the pressure generated is notrelieved by allowing the foam material 88 to expand in a directionsubstantially tangent to the winding s?"- n sr ani9 0 n o approxi p centcan be tolerated.

FIG. 12 is a flow chart illustrating the steps performed in constructinga rod.84 as described herein. Spaces between the rods 84 allow coolingfluid contained within the transformer casing 14 to flow between thewinding tube 80 and the core leg 82.

Since numerouschanges may-be made in the above described apparatus, andsince different embodiments of the invention may be made withoutdeparting from the spirit thereof, it is intended that all of the mattercontained in theforegoing description, or shown in the accompanyingdrawing, shall be interpreted as illustrative rather than limiting.

We claim as our invention:

1. A transformer comprising:

a magnetic core;

a winding structure disposed around said core;

a frame structure disposed around said core; and

a plurality of support blocks located between said core and said framestructure, said support blocks being constructed substantially of rigidplastic foam material, each of said support blocks having a first facepositioned tightly against a first portion of said frame structure and asecond face positioned tightly against a portion of said core.

2. The transformer of claim 1 wherein the rigid plastic foam material isenclosed within a container constructed of an expandable material. I

3. The transformer of claim 2 wherein the expandable material comprisesnitrile rubber.

4. The transformer of claim 1 wherein the first portion of the framestructure comprises a punching brace, and wherein each of the supportblocks has a third face positioned tightly against an end frame of theframe structure, the portion of the core adjacent the second face ofeach support block having a stepped surface, and the second face of eachsupport block being stepped to conform to the shape of the core surface.

5. A transformer comprising:

a magnetic core;

a frame structure disposed around said core;

a winding structure having a winding tube disposed around a portion ofsaid core; and

a plurality of support rods located between said core and said windingtube, each of said support rods being constructed of rigid plastic foammaterial enclosed within a tubular member, each of said rods beingpositioned tightly against said core and winding tube.

6. The transformer of claim 5 wherein the tubular member is constructedof a flexible, substantially nonexpandable material.

7. The transformer of claim 6 wherein the flexible, substantiallynon-expandable material comprises glass fiber reinforced epoxy.

8. The transformer of claim 5 wherein the outside circumference of eachtubular member is greater than a dimension equal to 1rd, wherein d isequal to the diameter of a circle which is tangent to the core and tothe winding tube at substantially the same points where the tubularmember contacts the core and winding tube.

9. The transformer of claim 5 wherein legs of the magnetic core have acruciform cross-sectional shape.

10. A method of constructing a transformer having a frame structuredisposed around a magnetic core, said method comprising the steps of:

positioning a mold between the core and the frame structure;

inserting an expandable plastic foam material into an expandablecontainer;

forming the expandable container containing the plastic foam materialwith the mold; and removing the mold from around the container after theplastic foam has become rigid.

11. A method of constructing a transformer having a winding structuredisposed around a magnetic core, said winding structure including awinding tube, said method comprising the steps of:

selecting a flexible, substantially non-expandable tubular member havinga suitable outside dimension; inserting the tubular member between thecore and the winding tube;

inserting an expandable plastic foam material into said tubular member;and

allowing the foam material to expand and flex the tubular member tightlyagainst the core and the winding tube.

1. A transformer comprising: a magnetic core; a winding structuredisposed around said core; a frame structure disposed around said core;and a plurality of support blocks located between said core and saidframe structure, said support blocks being constructed substantially ofrigid plastic foam material, each of said support blocks having a firstface positioned tightly against a first portion of said frame structureand a second face positioned tightly against a portion of said core. 2.The transformer of claim 1 wherein the rigid plastic foam material isenclosed within a container constructed of an expandable material. 3.The transformer of claim 2 wherein the expandable material comprisesnitrile rubber.
 4. The transformer of claim 1 wherein the first portionof the frame structure comprises a punching brace, and wherein each ofthe support blocks has a third face positioned tightly against an endframe of the frame structure, the portion of the core adjacent thesecond face of each support block having a stepped surface, and thesecond face of each support block being stepped to conform to the shapeof the core surface.
 5. A transformer comprising: a magnetic core; aframe structure disposed around said core; a winding structure having awinding tube disposed around a portion of said core; and a plurality ofsupport rods located between said core and said winding tube, each ofsaid support rods being constructed of rigid plastic foam materialenclosed within a tubular member, each of said rods being positionedtightly against said core and winding tube.
 6. The transformer of claim5 wherein the tubular member is constructed of a flexible, substantiallynon-expandable material.
 7. The transformer of claim 6 wherein theflexible, substantially non-expandable material comprises glass fiberreinforced epoxy.
 8. The transformer of claim 5 wherein the outsidecircumference of each tubular member is greater than a dimension equalto pi d, wherein ''''d'''' is equal to the diameter of a circle which istangent to the core and to the winding tube at substantially the samepoints where the tubular member contacts the core and winding tube. 9.The transformer of claim 5 wherein legs of the magnetic core have acruciform cross-sectional shape.
 10. A method of constructing atransformer having a frame structure disposed around a magnetic core,said method comprising the steps of: positioning a mold between the coreand the frame structure; inserting an expandable plastic foam materialinto an expandable container; forming the expandable containercontaining the plastic foam material with the mold; and removing themold from around the container after the plastic foam has become rigid.11. A method of constructing a transformer having a winding structuredisposed around a magnetic core, said winding structure including awinding tube, said method comprising the steps of: selecting a flexible,substantially non-expandable tubular member having a suitable outsidedimension; inserting the tubular member between the core and the windingtube; inserting an expandable plastic foam material into said tubularmember; and allowing the foam material to expand and flex the tubularmember tightly against the core and the winding tube.